The large scale burning of fossil fuels for electricity generation and other industrial processes, such as natural gas processing, ammonia production, cement manufacture, etc., results in the release of greenhouse gases, such as carbon dioxide, into the atmosphere. Electricity generation and industrial processes are the main sources of carbon dioxide emissions in most industrialised nations, and by far the largest single source of carbon dioxide emissions is fossil fuel based electricity generation, whether that be from coal, oil or natural gas.
In recent times, considerable attention and political pressure has been applied on organisations and individuals to reduce the amount of carbon dioxide that is released into the atmosphere. One way this can be done is to capture the emitted carbon dioxide before it is released into the atmosphere. The aim of so called “carbon capture” processes is to capture, separate and purify the emitted carbon dioxide so that it can subsequently be sent off to storage, in which case it is effectively taken out of the atmosphere.
Technologies for capturing carbon dioxide from electricity generation include post-combustion capture, pre-combustion capture, and oxy-firing.
In post-combustion capture, carbon dioxide is separated from the flue gas after fuel (coal or natural gas) is burnt. The main post-combustion products from sweetened natural gas (NG) or liquefied natural gas (LNG) fired power plants are nitrogen oxide gases and carbon oxide gases. Waste product output streams from NG plants have relatively low carbon dioxide content (3-5%), but in some cases this is increased by burning the NG in oxygen rather than air. Regardless, the output stream is at atmospheric and/or low pressure and comprises [CO2]Air>˜3-5% carbon dioxide if the fuel was burnt in air and [CO2]Oxy>70% if the fuel was burnt in oxygen.
Prior art techniques for capturing carbon dioxide utilize a chemical capture process in which the carbon dioxide in the waste stream is captured with an amine based solvent absorber. However, the amine based solvents that are typically used, such as methyl-ethanolamine (MEA) and methyl-diethanolamine (MDEA), are toxic, they decompose over time, and the efficiency of capture of carbon dioxide at low partial pressures is poor. Large columns are utilized for these prior art solvent carbon capture processes wherein the solvent is dispersed in a shower head configuration. Such configurations are limited in surface area contact of solvent with incoming waste product flue gas. Furthermore, post-combustion carbon dioxide capture processes based on absorption of carbon dioxide by a solvent have high energy requirements which result in an efficiency penalty on the power cycle. For MEA solvent based processes, cooling of the flue gas is necessary for absorption. Heat energy is then necessary to regenerate the solvent and also the steam that is used for stripping the carbon dioxide.
There is a need for alternative carbon capture processes that can be used to capture carbon dioxide and other carbon gases, such as carbon monoxide, from the output stream of power plants, such as natural gas fired gas turbine power plants.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.